Skin aging is a progressive phenomenon that occurs over time and can be affected by lifestyle factors, such as alcohol consumption, tobacco, and sun exposure. Aging of the facial skin can be characterized by atrophy, slackening, and fattening. Atrophy corresponds to a massive reduction of the thickness of skin tissue. Slackening of the subcutaneous tissues leads to an excess of skin and ptosis and leads to the appearance of drooping cheeks and eyelids. Fattening refers to an increase in excess weight by swelling of the bottom of the face and neck. These changes are typically associated with dryness, loss of elasticity, and rough texture.
Hyaluronan, also known as hyaluronic acid (“HA”), is a non-sulfated glycosaminoglycan that is distributed widely throughout the human body in connective, epithelial, and neural tissues. Hyaluronan is abundant in the different layers of the skin, where it has multiple functions such as, e.g., to ensure good hydration, to assist in the organization of the extracellular matrix, to act as a filler material; and to participate in tissue repair mechanisms. However, with age, the quantity of hyaluronan, collagen, elastin, and other matrix polymers present in the skin decreases. For example, repeated exposed to ultra violet light, e.g., from the sun, causes dermal cells to both decrease their production of hyaluronan as well as increase the rate of its degradation. This hyaluronan loss results in various skin conditions such as, e.g., imperfects, defects, diseases and/or disorders, and the like. For instance, there is a strong correlation between the water content in the skin and levels of hyaluronan in the dermal tissue. As skin ages, the amount and quality of hyaluronan in the skin is reduced. These changes lead to drying and wrinkling of the skin.
Dermal fillers are useful in treating soft tissue condition and in other skin therapies because the fillers can replace lost endogenous matrix polymers, or enhance/facilitate the function of existing matrix polymers, in order to treat these skin conditions. In the past, such compositions have been used in cosmetic applications to fill wrinkles, lines, folds, scars, and to enhance dermal tissue, such as, e.g., to plump thin lips, or fill-in sunken eyes or shallow cheeks. One common matrix polymer used in dermal filler compositions is hyaluronan. Because hyaluronan is natural to the human body, it is a generally well tolerated and a fairly low risk treatment for a wide variety of skin conditions.
Originally, compositions comprising hyaluronan where made from naturally occurring polymers, which exist in an uncrosslinked state. Although exhibiting excellent biocompatibility and affinity for water molecules, naturally occurring hyaluronan exhibits poor biomechanical properties as a dermal filler. One primary reason is that because this polymer is uncrosslinked, it is highly soluble and, as such, is cleared rapidly when administered into a skin region. This in vivo clearance is primarily achieved by rapid degradation of the polymers, principally enzymatic degradation via hyaluronidase and chemical degradation via free radicals. Thus, while still in commercial use, compositions comprising uncrosslinked hyaluronan polymers tend to degrade within a few days after administration and thus require fairly frequent reinjection to maintain their skin improving effect.
To minimize the effect of these in vivo degradation pathways, matrix polymers are crosslinked to one another to form a stabilized hydrogel. Because hydrogels comprising crosslinked matrix polymers are a more solid substance, dermal fillers comprising such hydrogels remain in place at the implant site longer. In addition, these hydrogels are more suitable as a dermal filler because it is more solid nature improves the mechanical properties of the filler, allowing the filler to better lift and fill a skin region. Hyaluronan polymers are typically crosslinked with a crosslinking agent to form covalent bonds between hyaluronan polymers. Such crosslinked polymers form a less water soluble hydrogel network that is more resistant to degradation, and thus requires less frequent reinjection, than the non-crosslinked hyaluronan compositions.
Current dermal fillers can be associated with a variety of side effects. For example, administration of a dermal filler to an individual is typically performed using a syringe or needle. Such administration could result in one or more unwanted side-effects, such as, e.g., pain and discomfort to the individual, bleeding in and under the site of administration, and itching, inflammation and irritation in the vicinity of the administration site during and after the administration of the dermal filler. The dermal fillers disclosed in the present specification address these and other unwanted side-effects by providing hydrogel compositions comprising agents that reduce, step, or prevent one or more of these side-effects.
Additionally, a dermal filler formulation must be capable of withstanding sterilization which is a strict requirement before the product can be sold (the product must be sterile). Sterilization can be carried out by steam sterilization, filtration, microfiltration, gamma radiation, ETO light or by a combination of these methods. It is known that a dermal filler can be steam sterilized (autoclaved) without substantial degradation of physical properties, but when a dermal filler formulation contains an additional labile ingredient (such as an antioxidant, anti-itch agent, an anti-cellulite agent, an anti-scarring agent, an anti-inflammatory agent, an anesthetic agent, an anti-irritant agent, a vasoconstrictor, a vasodilator, an anti-hemorrhagic agent like a hemostatic agent or anti-fibrinolytic agent, a desquamating agent, a tensioning agent, an anti-acne agent, a pigmentation agent, an anti-pigmentation agent, or a moisturizing agent) the entire dermal filler formulation or at least the additional (heat labile) agent is traditionally sterilized by a non-heat treatment such as by a filtration sterilization method. Thus, a known dermal filler product (REVITACARE® Bio-Revitalisation, REVITACARE® Laboratory, Saint-Ouen-l'Aumône, France) is sold in two separate vials or containers, one vial containing the HA (which is autoclave sterilized)) and the second vial containing any additional ingredients (the second vial contents are sterilized by filtration). Another known dermal filler product NCTF® 135HA (Laboratoires Filorga, Paris, France) is sold in a single container holding both hyaluronan and any additional ingredients, all having been sterilized by microfiltration. The dermal fillers disclosed in the present specification addresses this issue by developing dermal fillers that are entirely sterilized by a heat treatment, i.e., in some embodiments of this invention, none of the components are sterilized solely using a non-heat treatment such as, e.g., filtration.